Thin film transistors (TFTs) are a class of field effect transistors (FETs), in which the current through the channel is modulated on the same basic principle as in the Metal Oxide Semiconductor Field Effect Transistor (MOSFET). Unlike the MOSFET where the substrate material is the bulk semiconductor, such as the single crystalline silicon, in the TFT, the thin film of semiconductor materials is deposited on substrates such as glasses or polymers to form the channel layers of TFTs. TFTs are emerging for large area electronics, particularly, the display systems. Hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) TFTs are current industry standard for the switching and drive circuitry of monolithic active matrix liquid crystal display (AMLCD) and active matrix organic light emitting diode (AMOLED) technology.
Referring now to FIG. 1, a conventional display pixel 100 used in AMOLEDs generally has two amorphous silicon thin film transistors (“TFTs”) 102, 104, a storage capacitor 106, and an organic light emitting diode (“OLED”) 108. The two TFTs include a switching TFT 104 and a driver TFT 102. The TFTs 102, 104, interconnect lines, and storage capacitor 106 are the circuitry that drive the OLED 108, and are referred to as backplane of the display. The OLED 108 is the light emitting element, and is the frontplane of the display. During operation, the switching TFT 104 is turned on and the data signal can be propagated to a storage node 110. This action charges up the storage capacitor 106 and sets up the gate voltage of the driver ITT 102. The driver TFT 102 converts the data signal into the electrical current. The resulting brightness of the OLED 108 is determined by the output current of the driver TFT 102. The conventional pixel 100 uses a storage capacitor 106 to hold the electrical charges in the pixel. The charges stored in the capacitor 106 constantly leak out and therefore, refresh cycles are required to maintain a static image. Such refresh cycles introduce the power consumption of the display system. Because of the low mobility of amorphous silicon, conventional TFTs cannot drive large area display systems with frame rates higher than 120 Hz. The requirement of mobility is even higher for displays with higher resolution.
Recently, three-dimensional (“3D”) displays with 240 Hz frame rates have been produced. However, higher frame rates of 480 Hz are required to improve picture quality because a 3D display must project two or more pictures alternately for left and right eyes. Accordingly, there is as need in the art for a pixel structure that can support the frame requirement of new 3D displays, while not increasing power consumption in comparison to existing pixel structures.